Background: The relationship between physical activity at work and risk of fetal growth restriction is controversial. For the most part, previous studies investigated the effect of work activity on birthweight alone. We evaluated the impact of type of occupation and physical effort at work on the risk of ultrasonographically confirmed fetal growth retardation among nulliparous women.
Methods: We compared the characteristics of work and the intensity of occupational fatigue (work posture, weekly working hours, physical effort at work) in 349 patients with ultrasonographically confirmed fetal growth retardation and 698 control pregnancies with appropriate fetal growth. Physical demands at work were evaluated by interview at birth. Logistic regression analysis was used to evaluate the association of employment status, type of occupation, and intensity of occupational fatigue with the risk of fetal growth retardation, correcting for potential confounders (maternal age, pre-pregnancy body mass index, mean weight gain in pregnancy, education, partner's social status, smoking in pregnancy, alcohol use, illicit drug use, time of stopping work, and hypertension).
Results: After adjusting for confounding, the risk of fetal growth retardation was similar between unemployed and formally employed women at the beginning of pregnancy (OR = 1.26; 95% confidence interval = 0.86 - 1.83). However, manual workers were at slightly higher risk of IUGR than not formally employed women (OR = 1.81; 95% CI = 1.15 - 2.85). Among formally employed women, standing or walking at work, and working > or = 30 hours a week were not significantly associated with IUGR. Finally, the risk of IUGR was significantly higher (OR = 2.46; 95% CI = 1.36 - 4.21) among women reporting moderate-to-heavy as compared to light physical effort at work.
Conclusion: Formal employment at the beginning of pregnancy is not associated with an increased risk of IUGR. However, moderate-to-heavy physical effort at work seems to increase the risk of sonographically confirmed fetal growth retardation.